Fuel control system having an auxiliary circuit for correcting the signals generated by the pressure sensor during transient operating conditions

Abstract

A fuel control system having an auxiliary circuit for correcting the signals generated by a pressure sensor under transient operating conditions is disclosed. The circuit generates a pressure correction signal directly proportional to the first time derivative of the intake manifold pressure and inversely proportional to rotational speed of the engine which is added to the signal generated by the pressure sensor. The added signals are utilized by the electronic control unit for computing the fuel requirements of the engine to maintain a constant fuel/air ratio during steady state and transient operating conditions.

What is claimed is: 
     
       1. An electronic fuel injection system for an internal combustion engine comprising: engine sensor means for generating signals indicative of engine operating conditions, said sensor means including pressure sensor means for generating a pressure signal indicative of engine air intake manifold pressure, and speed sensor means for generating a speed signal indicative of engine operating speed;   pressure signal correction circuit means for generating a corrected pressure signal having a value equal to the sum of said pressure signal and a correction signal generated in response to said pressure signal and said speed signal, when the pressure signal is changing and indicative of a transient condition;   electronic control unit means for generating electrical signals indicative of engine fuel requirements in response to signals generated by said engine sensors, including said speed signal and said corrected pressure signal; and   fuel delivery means for delivering fuel in response to the signals generated by said electronic control unit means.   
     
     
       2. The electronic fuel injection system of claim 1 wherein said pressure signal correction circuit means comprises: means for generating said pressure correction signal having a value directly proportional to the first time derivative of the pressure signal and inversely proportional to the speed signal; and   means for adding said pressure correction signal to the pressure signal to generate said corrected pressure signal.   
     
     
       3. The electronic fuel injection system of claim 2 wherein said electronic control unit generates said electrical signals as a function of engine air, wherein air flow is given by the equation; ##EQU7## where; W a  = engine air flow D mv  = engine volumetric displacement (in 3  /Rad)   N = engine speed (Rad/sec)   P m  = manifold pressure (lbs/sq. inch absolute)   R = gas constant (inch lb/lb °R)   t = gas temperature (°R) and wherein, under transient operating conditions the actual engine air flow as a function of engine speed and manifold air pressure is given by the equation; ##EQU8## where; V = manifold volume (inches 3 )     k = ratio of specific heat   dP m  /dt = first time derivative of the manifold pressure said means for generating a pressure correction signal generates a signal having a value V/KND mv  (dP m  dt) and;     said means for adding generates a signal having a value P m  V/kND mv  (dP.sub. m /dt).   
     
     
       4. In combination with an electronic fuel injection system for an internal combustion engine, said electronic fuel injection system having engine sensors generating signals indicative of engine operating conditions, including pressure sensor means generating pressure signals indicative of engine air intake manifold pressure and speed sensor means generating speed signals indicative of engine speed, and an electronic control unit generating electrical signals indicative of engine fuel requirements, and at least one injector means for delivering fuel in response to the electrical signals generated by the electronic control unit, a pressure signal correction circuit means electrically disposed between said pressure sensor and said electronic control unit for generating corrected pressure signals in response to said pressure signals and said speed signals, said corrected pressure signal being indicative of the actual engine air flow during steady state and transient operating conditions. 
     
     
       5. The combination of claim 4 wherein the electronic control unit generates said electrical signals as a function of engine air flow determinable from the equation: ##EQU9## where; W a  = engine air flow to the engine D mv  = engine volumetric displacement (inch 3  /Rad)   N = engine speed (Rad/sec)   P m  = manifold air pressure (lbs/sq inch absolute)   R = gas constant (inch lb/lb °R)   t = gas temperature (°R) and wherein the actual engine air flow as a function of engine speed and manifold air pressure is given by the equation: ##EQU10## where: V = manifold volume (inches 3 )     K = ratio of specific heats   dP m  /dt = first derivative of the manifold pressure P m  with respect to time said pressure signal correction circuit means generates corrected pressure signals indicative of the sum of said pressure signal and a pressure correction signal, said pressure correction signal having a value directly proportional to the first derivative of the time variations of said pressure signal and inversely proportional to said speed signal.     
     
     
       6. The combination of claim 5 wherein said pressure correction circuit comprises: circuit means for generating said pressure correction signal in response to the generated pressure and speed signals; and   summing means receiving the generated pressure signal and said correction signal to generate said corrected pressure signal.   
     
     
       7. The combination of claim 5 wherein said circuit means for generating said correction signal comprises: circuit means receiving the generated pressure signal for generating a derivative signal indicative of the first time derivative of the pressure signal and;   circuit means dividing said derivative signal by said speed signal to generate said correction signal.   
     
     
       8. The combination of claim 7 wherein said circuit means for generating a correction signal generates a singal having a value V/kND mv  (dP m  /dt). 
     
     
       9. The combination of claim 7 wherein the air pressure being detected by the pressure sensor has noise, said noise having a frequency proportional to the engine speed, said pressure signal correction circuit means further includes a low pass filter circuit to reduce the sensitivity of the circuit means for generating a derivative signal to the pressure signals generated by the pressure sensor in response to the noise of the air pressure being detected. 
     
     
       10. In an electronic fuel injection equipped internal combustion engine system having an internal combustion engine, engine sensors generating signals indicative of the engine's operating conditions, including pressure sensor means generating pressure signals indicative of the pressure in the engine's air intake manifold and speed sensor means generating speed signals indicative of the rotational speed of the engine, an electronic control unit responsive to at least said pressure and said speed signals for generating electrical signals indicative of the engine's fuel requirements, and at least one injector means for injecting fuel into the engine in response to the electrical signals generated by the electronic control unit, an improvement for correcting the pressure signals generated by the pressure sensor means during transient modes of operation comprising: means responsive to the signals generated by the pressure sensor means and the speed sensor means for generating pressure correction signals to compensate for the compressibility of air intake manifold when the engine is in a transient mode of operation; and   means for summing said pressure correction signals to said pressure signals to generate a corrected pressure signal;   wherein said electronic control unit generates said electrical signals in response to said corrected pressure signal.   
     
     
       11. The improvement of claim 10 wherein the electronic control unit generates said electrical signals as a function of the air flow to the engine per engine revolution in accordance with the equation: ##EQU11## where: W a  = the air flow into the engine D mv  = volumetric displacement of the engine (inch 3  /Rad)   N = engine speed (Rad/sec)   P m  = manifold air pressure (lbs/sq inch absolute)   R = gas constant (inch lb/lb °R)   t = gas temperature (°R) and wherein the actual air flow to the engine per revolution is given by the equation: ##EQU12## where: V = manifold volume (inches 3 )     k = ratio of specific heats   S = Laplace Operator (d/dt) said means for generating said correction signal generates a signal proportional to SP m  /N.     
     
     
       12. The improvement of claim 11 wherein said means for generating said correction signal generates a singal having a value VSP m  /kND mv . 
     
     
       13. The improvement of claim 11 wherein said means for generating said correction signal includes: means receiving said pressure signal for generating a derivative signal indicative of the first time derivative of said pressure signal; and   means for dividing said derivative signal by said speed signal to generate said correction signal.   
     
     
       14. The improvement of claim 13 wherein said means for generating said derivative signal includes: a capacitor receiving said pressure signal;   an operational amplifier having an input connected to said capacitor and an output; and   a feedback resistance having one end connected to the input of said operation amplifier and the other end connected output of said operational amplifier.   
     
     
       15. The improvement of claim 14 wherein said engine has at least one cylinder, and at least one air intake valve associated with said at least one cylinder, said air intake valve periodically opening to admit air from the manifold into said at least one cylinder and wherein the pressure in the manifold fluctuates with the opening and closing of said at least one valve generating noise superimposed on the generated pressure signal, said means for generating a derivative signal further includes a low pass filter to remove the noise superimposed on the pressure signal generated by the opening and closing of the engine's air intake valves. 
     
     
       16. The improvement of claim 15 wherein said low pass filter comprises a capacitance in parallel with said feedback resistance. 
     
     
       17. The improvement of claim 11 wherein said means for generating said correction signal includes: means for generating a derivative signal indicative of the first derivative of said pressure signal;   means for generating an inverted signal having a value inversely proportional to said speed signal; and   means for multiplying said derivative signal by said inverted signal to generate said correction signal.   
     
     
       18. The improvement of claim 17 wherein said engine has at least one cylinder, and at least one air intake valve associated with said at least one cylinder, said air intake valve periodically opening to admit air from the manifold into said at least one cylinder, and wherein the pressure in the manifold fluctuates with the opening and closing of said at least one valve generating noise superimposed on the generated pressure signal, said means for generating a derivative signal further includes a low pass filter to remove the noise superimposed on the pressure signal generated by the opening and closing of the engine's valves. 
     
     
       19. The improvement of claim 11 wherein said pressure sensor means is a variable inductance transformer having primary and secondary electrical windings and means for changing the value of the inductance in said windings as a function of the manifold pressure, and wherein said electronic control unit generates a first signal communicated to the pressure sensor's primary winding and generates said electrical signals indicative of the engine's fuel requirements in response to the signals induced in the secondary winding wherein said induced signals are indicative of the pressure in the intake manifold, said means for summing is means for combining said correction signal to said induced signal to generate said corrected pressure signal. 
     
     
       20. The improvement of claim 19 wherein said means for combining said correction signal to said induced signal is a means for adding said correction signal to said first signal. 
     
     
       21. A circuit for use in combination with a pressure sensor and an internal combustion engine having an air intake manifold and electronic fuel control to correct the signals generated by the pressure sensor during transient operating conditions, wherein said pressure sensor generates pressure signals indicative of the pressure in the engine's air intake manifold and said engine has at least one other sensor generating a speed signal indicative of the rotational speed of the engine comprising: differentiator circuit means receiving said pressure signals and said speed signals for generating pressure correction signals having a value proportional to the first time derivative of the pressure in the intake manifold and inversely proportional to the rotational speed of the engine; and   means for summing said pressure correction signal to said pressure signal to generate a corrected pressure signal.   
     
     
       22. In combination with a utilization device having a fluid intake manifold and a pressure sensor generating a signal indicative of the fluid pressure in the intake manifold, a circuit for correcting the pressure signal generated by a pressure sensor for the compressibility of the fluid flowing in the intake manifold of the utilization device comprising: sensor means generating speed signals indicative of the speed of fluid flow through the utilization device;   circuit means receiving said pressure signals and said speed signals for generating a pressure correction signal having a value proportional to the first time derivative of the pressure signal and inversely proportional to the speed signal; and   means for adding said pressure correction signal to said pressure signal.   
     
     
       23. A method for correcting the pressure signals generated by a pressure sensor monitoring the pressure in the intake manifold of an internal combustion engine for the compressibility of the air during transient modes of operation comprising the steps of: detecting the pressure in the engine's intake manifold with a pressure sensor to generate pressure signals;   differentiating the pressure signals generated by the pressure sensor to generate a differentiated signal having a value proportional to the first time derivative of pressure in the intake manifold;   detecting the rotational speed of the engine to generate a speed signal;   dividing the differentiated signal by said speed signal to generate a correcton signal having a value proportional to the first time derivative of the pressure and inversely proportional to the rotational speed of the engine; and   adding said correction signal to pressure signal to generate a pressure signal compensated for the compressibility of the air.